Magnetic core with multiple teeth having four different teeth tips axially overlapping

ABSTRACT

A magnetic core for an electric motor has a ring-shaped yoke, teeth extending outwardly from the yoke, and a tooth tip extending from a distal end of each tooth. The core is formed from curved or coils strip laminations having teeth arranged in tooth groups. Each group has four tooth types arranged sequentially. Each tooth has left and right half tooth tips. The length of the half tooth tips vary according to tooth type. When assembled, first type tooth overlap with third type teeth and second type teeth overlap with fourth type teeth, whereby the opening of the winding slot is narrowed compared to laminations having all identical teeth.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims priority under 35 U.S.C.§ 119(a) from Patent Application No. 201510280698.1 filed in ThePeople's Republic of China on May 27, 2015, and from Patent ApplicationNo. 201610078383.3 filed in The People's Republic of China on Feb. 3,2016, the entire contents of both are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to an electric motor and in particular, to amagnetic core of the electric motor.

BACKGROUND OF THE INVENTION

A conventional magnetic core for a motor includes a ring-shaped yoke anda plurality of teeth extending outwardly from the yoke. Each tooth has atooth tip at a distal end thereof. Each tooth tip has a left half toothtip and a right half tooth tip. The length of the left and right halftooth tips are measured in the circumferential direction of the yoke andare equal.

The magnetic core is made by stacking a plurality of ring-shaped corelaminations. If the core laminations are directly punched from sheetmaterials, a large amount of waste material will be produced.

In an improved solution, an elongated core lamination is punched from arectangular sheet material, which elongated core lamination includes aconnection portion and a plurality of teeth extending from theconnecting portion. The connecting portion is bent to form a ring-shapedcore lamination. A disadvantage of this method is that the length of thetooth tip is limited, which results in an unduly large opening of thewinding slot of the magnetic core.

SUMMARY OF THE INVENTION

Hence there is a desire for a magnetic core which has relatively lowmaterial wastage and narrow winding slot openings.

Accordingly, in one aspect thereof, the present invention provides amagnetic core for an electric motor, comprising: a ring-shaped yoke;teeth extending outwardly from the yoke, and a tooth tip extending froma distal end of each tooth in a circumferential direction of the core,each tooth tip having a left half tooth tip and a right half tooth tip;wherein the magnetic core has a plurality of lamination layers, eachlamination layer comprising: multiple teeth having a first type tooth, asecond type tooth, a third type tooth and a fourth type tooth, the lefthalf tooth tip of the first type tooth being a short tooth tip, theright half tooth tip of the first type tooth being a long tooth tip, theleft and right half tooth tips of the second type tooth being both shorttooth tips, the left half tooth tip of the third type tooth being a longtooth tip, the right half tooth tip of the third type tooth being ashort tooth tip, the left and right half tooth tips of the fourth typetooth being both long tooth tips; and wherein, in an axial direction ofthe motor, the first type tooth of at least one lamination layeroverlaps with the third type tooth of another lamination layer, thesecond type tooth of the at least one lamination layer overlaps with thefourth type tooth of the another lamination layer, the third type toothof the at least one lamination layer overlaps with the first type toothof the another lamination layer, and the fourth type tooth of the atleast one lamination layer overlaps with the second type tooth of theanother lamination layer.

Preferably, each lamination layer includes an even number of teeth; themagnetic core is formed by stacking multiple layers of first corelaminations and multiple layers of second core laminations and, in themotor axial direction, the first type tooth, second type tooth, thethird type tooth and fourth type tooth of the first core laminationoverlap with the third type tooth, fourth type tooth, first type tooth,and second type tooth of the second core lamination, respectively.

Preferably, the first type tooth, second type tooth, the third typetooth and fourth type tooth form one tooth group, the magnetic coreincludes two types of lamination layers, a first type of core laminationis formed by cutting off a first half of a first tooth group from a corelamination having sequentially arranged k+1 tooth groups, and a secondtype of core lamination is formed by cutting off a second half of a lasttooth group from a core lamination having sequentially arranged k+1tooth groups, where k is an integer greater than zero; the first type ofcore lamination and the second type of core lamination are alternatelyarranged.

Preferably, wherein each tooth group satisfies one of the followingconditions: (a) each tooth group includes multiple first type teeth, onesecond type tooth, multiple third type teeth, and one fourth type tooththat are sequentially arranged, wherein the number of the first typeteeth is the same as the number of the third type teeth; (b) each toothgroup includes one second type tooth, multiple third type teeth, onefourth type tooth, and multiple first type teeth that are sequentiallyarranged, wherein the number of the first type teeth is the same as thenumber of the third type teeth; (c) each tooth group includes multiplethird type teeth, one fourth type tooth, multiple first type teeth, andone second type tooth that are sequentially arranged, wherein the numberof the first type teeth is the same as the number of the third typeteeth; (d) each tooth group includes one fourth type tooth, multiplefirst type teeth, one second type tooth, and multiple third type teeththat are sequentially arranged, wherein the number of the first typeteeth is the same as the number of the third type teeth.

Preferably, each lamination layer has S teeth, wherein multiple firsttype teeth, one second type tooth, multiple third type teeth and onefourth type tooth are sequentially arranged to form one tooth group, thenumber of the third type teeth is the same as the number of the firsttype teeth in each tooth group, and each tooth group has T teeth, with Sand T satisfying the following relation: S/T=N+½, where N is a positiveinteger and T is an even number.

Preferably, a sum of the length of the right half tooth tip of the firsttype tooth and the length of the left half tooth tip of the second typetooth, a sum of the length of the right half tooth tip of the secondtype tooth and the length of the left half tooth tip of the third typetooth, a sum of the length of the right half tooth tip of the third typetooth and the length of the left half tooth tip of the fourth type toothtip, and a sum of the length of the right half tooth tip of the fourthtype tooth and the length of the left half tooth tip of the first typetooth tip are substantially the same.

Preferably, the magnetic core is made by spirally rolling an elongatedsheet material multiple turns, with each turn forming one laminationlayer of the magnetic core.

Preferably, each lamination layer of the magnetic core is made bybending an individual sheet material.

According to a second aspect, the present invention provides a methodfor making a magnetic core for an electric motor, comprising thefollowing steps: step S1: forming a plurality of elongated sheetmaterials by punching, with each sheet material including a connectingportion and a plurality of teeth extending from the connecting portion,each tooth including a tooth tip extending from a distal end of thetooth to two sides thereof, the tooth tip including a left half toothtip and a right half tooth tip; each sheet material including aplurality of groups each having a first type tooth, a second type tooth,a third type tooth and a fourth type tooth that are sequentiallyarranged, the left half tooth tip of the first type tooth being a shorttooth tip, the right half tooth tip of the first type tooth being a longtooth tip, the left and right half tooth tips of the second type toothare both short tooth tips, the left half tooth tip of the third typetooth being a long tooth tip, the right half tooth tip of the third typetooth being a short tooth tip, the left and right half tooth tips of thefourth type tooth being both long tooth tips; step S3: bending eachsheet material into a ring-shaped core lamination, with the connectingportions of all sheet materials making a ring-shaped yoke and the teethof each sheet material extending outwardly from the yoke; and step S4:stacking multiple layers of ring-shaped core laminations, with the firsttype tooth of at least one lamination layer overlapping with the thirdtype tooth of another lamination layer, the second type tooth of the atleast one lamination layer overlapping with the fourth type tooth of theanother lamination layer, the third type tooth of the at least onelamination layer overlapping with the first type tooth of the anotherlamination layer, and the fourth type tooth of the at least onelamination layer overlapping with the second type tooth of the anotherlamination layer.

Preferably, at step S1, each lamination layer after being punched has Steeth, wherein multiple first type teeth, one second type tooth,multiple third type teeth and one fourth type tooth that aresequentially arranged to form one tooth group, and each tooth group hasT teeth, with S and T satisfying the following relation: S/T=N+½, whereN is a positive integer and T is an even number; and at step S3, thefirst type tooth, second type tooth, third type tooth and fourth typetooth of a first type sheet material overlap with the third type tooth,fourth type tooth, first type tooth and second type tooth of a secondtype sheet material, respectively.

Preferably, at step S3, the first type sheet material and the secondtype sheet material are alternately arranged.

Preferably, at step S1, the sheet material is first punched to have 2k+1tooth groups, and the sheet material having 2k+1 tooth groups is cut atthe (k+1)th tooth group, thus obtaining the first type sheet materialand the second type sheet material.

Preferably, at step S1, each tooth group satisfies one of the followingconditions: (a) each tooth group includes multiple first type teeth, onesecond type tooth, multiple third type teeth, and one fourth type tooththat are sequentially arranged, wherein the number of the first typeteeth is the same as the number of the third type teeth; (b) each toothgroup includes one second type tooth, multiple third type teeth, onefourth type tooth, and multiple first type teeth that are sequentiallyarranged, wherein the number of the first type teeth is the same as thenumber of the third type teeth; (c) each tooth group includes multiplethird type teeth, one fourth type tooth, multiple first type teeth, andone second type tooth that are sequentially arranged, wherein the numberof the first type teeth is the same as the number of the third typeteeth; (d) each tooth group includes one fourth type tooth, multiplefirst type teeth, one second type tooth, and multiple third type teeththat are sequentially arranged, wherein the number of the first typeteeth is the same as the number of the third type teeth.

According to a third aspect, the present invention provides a method formaking a magnetic core for an electric motor, comprising the followingsteps: step S1: forming a plurality of elongated sheet materials bypunching, with each sheet material including a connecting portion and aplurality of teeth extending from the connecting portion, each toothincluding a tooth tip extending from a distal end of the tooth to twosides thereof, the tooth tip including a left half tooth tip and a righthalf tooth tip; each sheet material including a plurality of groups ofteeth each having a first type tooth, a second type tooth, a third typetooth and a fourth type tooth that are sequentially arranged, the lefthalf tooth tip of the first type tooth being a short tooth tip, theright half tooth tip of the first type tooth being a long tooth tip, theleft and right half tooth tips of the second type tooth are both shorttooth tips, the left half tooth tip of the third type tooth being a longtooth tip, the right half tooth tip of the third type tooth being ashort tooth tip, the left and right half tooth tips of the fourth typetooth being both long tooth tips; step S2: stacking multiple sheetmaterials to form multiple layers of core laminations, with the firsttype tooth of at least one lamination layer overlapping with the thirdtype tooth of another lamination layer, the second type tooth of the atleast one lamination layer overlapping with the fourth type tooth of theanother lamination layer, the third type tooth of the at least onelamination layer overlapping with the first type tooth of the anotherlamination layer, and the fourth type tooth of the at least onelamination layer overlapping with the second type tooth of the anotherlamination layer; and step S3: bending the stacked multiple layers ofcore laminations into a ring shape, with the connecting portions of allsheet materials making a ring-shaped yoke, and the teeth of each sheetmaterial extending outwardly from the yoke.

According to a another aspect, the present invention provides a methodfor making a magnetic core for an electric motor, comprising thefollowing steps: step S1: forming an elongated sheet material bypunching, with the sheet material including a connecting portion and aplurality of teeth extending from the connecting portion, each toothincluding a tooth tip extending from a distal end of the tooth to twosides thereof, the tooth tip including a left half tooth tip and a righthalf tooth tip; the sheet material including a plurality of groups ofteeth each having a first type tooth, a second type tooth, a third typetooth and a fourth type tooth that are sequentially arranged, the lefthalf tooth tip of the first type tooth being a short tooth tip, theright half tooth tip of the first type tooth being a long tooth tip, theleft and right half tooth tips of the second type tooth are both shorttooth tips, the left half tooth tip of the third type tooth being a longtooth tip, the right half tooth tip of the third type tooth being ashort tooth tip, the left and right half tooth tips of the fourth typetooth being both long tooth tips; and step S2: spirally rolling thesheet material multiple turns, with each turn forming a lamination layerof the magnetic core, each lamination layer including a ring-shaped yokeand the teeth extending from the yoke; with the first type tooth of atleast one lamination layer overlapping with the third type tooth ofanother lamination layer, the second type tooth of the at least onelamination layer overlapping with the fourth type tooth of the anotherlamination layer, the third type tooth of the at least one laminationlayer overlapping with the first type tooth of the another laminationlayer, and the fourth type tooth of the at least one lamination layeroverlapping with the second type tooth of the another lamination layer.

Preferably, at step S2, each lamination layer has S teeth, wherein thefirst type tooth, second type tooth, third type tooth and fourth typetooth form one tooth group, and each tooth group has T teeth, with S andT satisfying the following relationship: S/T=N+½, where N is a positiveinteger and T is an even number; the last T/2 teeth of a previouslamination layer and the first T/2 teeth of a later lamination layerform one tooth group.

Preferably, at step S2, each tooth group satisfies one of the followingconditions: (a) each tooth group includes multiple first type teeth, onesecond type tooth, multiple third type teeth, and one fourth type tooththat are sequentially arranged; (b) each tooth group includes one secondtype tooth, multiple third type teeth, one fourth type tooth, andmultiple first type teeth that are sequentially arranged; (c) each toothgroup includes multiple third type teeth, one fourth type tooth,multiple first type teeth, and one second type tooth that aresequentially arranged; (d) each tooth group includes one fourth typetooth, multiple first type teeth, one second type tooth, and multiplethird type teeth that are sequentially arranged, wherein the number ofthe first type teeth is the same as the number of the third type teeth.

Preferably, at step S1, each tooth is formed with a tooth body extendingfrom the connecting portion, each tooth tip extends from a distal end ofthe tooth body to two sides thereof, and a sum of lengths of adjacenttooth tips of adjacent teeth is equal to or slightly less than adistance between the tooth bodies of the adjacent teeth.

In embodiments of the present invention, the core laminations of themagnetic core are formed from an elongated sheet material, which reducesthe material wastage. In the axial direction of the core, the long toothtip and short tooth tip overlap with each other, thus reducing the widthof the winding slot opening.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way ofexample only, with reference to figures of the accompanying drawings. Inthe figures, identical structures, elements or parts that appear in morethan one figure are generally labeled with a same reference numeral inall the figures in which they appear. Dimensions of components andfeatures shown in the figures are generally chosen for convenience andclarity of presentation and are not necessarily shown to scale. Thefigures are listed below.

FIG. 1 illustrates a core for an electric motor according one embodimentof the present invention.

FIG. 2 is an unrolled view of two adjacent core laminations of the coreof FIG. 1.

FIG. 3 illustrates a tooth group of the core of FIG. 2.

FIG. 4 and FIG. 5 illustrate two adjacent core laminations formed bybending the sheets of FIG. 2.

FIG. 6 illustrates a sheet material coiled to form a core according toanother embodiment of the present invention.

FIG. 7 illustrates an unrolled portion of a core lamination according toanother embodiment of the present invention.

FIG. 8 illustrates an unrolled portion of a core lamination according tostill another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 and FIG. 2, one embodiment of the present inventionprovides a magnetic core 100 for an electric motor, which includes aring-shaped yoke 10, teeth 20 extending outwardly from the yoke 10, andtooth tips 30 extending from distal ends of tooth body 22 of the teeth20 in a circumferential direction. The tooth tip 30 of each tooth 20includes a left half tooth tip 32 and a right half tooth tip 34. Thelength of the left half tooth tip 32 and the right half tooth tip 34 aremeasured in the circumferential direction of the yoke 10. The magneticcore 100 is made by stacking a plurality of core laminations 200 (FIG.2). The magnetic core 100 is made from a magnetically-conductivematerial and is preferably an iron core. Each lamination forming alamination layer of the core.

Referring to FIG. 2 and FIG. 3, a first lamination layer 200 a in FIG. 2is formed by cutting off a second half of the last tooth group fromsequentially arranged five tooth groups 210. A second lamination layer200 b in FIG. 2 is formed by cutting off a first half of the first toothgroup from sequentially arranged five tooth groups 210. In alternativeembodiments, each lamination layer may have more or less tooth groups.

As shown in FIG. 3, each tooth group 210 includes four sequentiallyarranged teeth including a first type tooth 1, a second type tooth 2, athird type tooth 3, and a fourth type tooth 4. The left half tooth tipof the first type tooth 1 is a short tooth tip, and the right half toothtip is a long tooth tip. The left and right half tooth tips of thesecond type tooth 2 are both short tooth tips. The left half tooth tipof the third type tooth 3 is a long tooth tip, and the right half toothtip is a short tooth tip. The left and right half tooth tips of thefourth type tooth 4 are both long tooth tips. Specifically, the firsttype tooth 1, the second type tooth 2, the third type tooth 3 and thefourth type tooth 4 satisfy the following conditions: (a) the length ofthe left half tooth tip of the first type tooth 1 is less than thelength of the left half tooth tip of the third type tooth 3, the lengthof the right half tooth tip of the first type tooth 1 is greater thanthe length of the right half tooth tip of the third type tooth 3, thelength of the left half tooth tip of the second type tooth 2 is lessthan the length of the left half tooth tip of the fourth type tooth 4,and the length of the right half tooth tip of the second type tooth 2 isless than the length of the right half tooth tip of the fourth typetooth 4.

In a first alternative embodiment, the second type tooth 2, the thirdtype tooth 3, the fourth type tooth 4 and the first type tooth 1 aresequentially arranged into a tooth group.

In a second alternative embodiment, the third type tooth 3, the fourthtype tooth 4, the first type tooth 1 and the second type tooth 2 aresequentially arranged into a tooth group.

In a third alternative embodiment, the fourth type tooth 4, the firsttype tooth 1, the second type tooth 2 and the third type tooth 3 aresequentially arranged into a tooth group.

Such structural arrangements can increase the material utilization rate.As shown in FIG. 2, when the core lamination is punched from a sheetmaterial, a large portion of the material can be used as the lamination,which reduces material wastage. In addition, when viewed from left tothe right in FIG. 2, after two adjacent lamination layers are stacked,the shorter left half tooth tip of the first type tooth 1 of the upperlamination layer 200 a overlaps with the longer left half tooth tip ofthe third type tooth of the lower lamination layer 200 b, the longerright half tooth tip of the first type tooth 1 of the upper laminationlayer 200 a overlaps with the shorter right half tooth tip of the thirdtype tooth of the lower lamination layer 200 b, thereby increasing theeffective length of the left half tooth tip and right half tooth tip ofeach tooth of the stator core, which can minimize the width of theopening of the winding slot and hence improve the motor performance.

In the description and claims, “overlap” refers to the overlapping ofprojections in a certain direction. For example, the overlapping of thefirst type tooth 1 of the upper lamination layer 200 a and the thirdtype tooth 3 of the lower lamination layer 200 b refers to theoverlapping of the projections of the first type tooth 1 and the thirdtype tooth 3 in the motor axial direction. The upper lamination layer200 a and the lower lamination layer 200 b may be two adjacent corelaminations, and also may be two core laminations that are not adjacentto each other.

As shown in FIG. 2, the relationship between the first type tooth 1, thesecond type tooth 2, the third type tooth 3, and the fourth type tooth4, preferably, satisfies the following conditions: a sum of the lengthsof adjacent tooth tips of adjacent teeth is close to (equal to orslightly less than) a distance between tooth bodies of adjacent teeth.In particular, a sum of the length of the right half tooth tip of thefirst type tooth 1 and the length of the left half tooth tip of thesecond type tooth 2, a sum of the length of the right half tooth tip ofthe second type tooth 2 and the length of the left half tooth tip of thethird type tooth 3, a sum of the length of the right half tooth tip ofthe third type tooth 3 and the length of the left half tooth tip of thefourth type tooth tip 4, and a sum of the length of the right half toothtip of the fourth type tooth 4 and the length of the left half tooth tipof the first type tooth tip 1 are substantially the same and each equalto or slightly less than a distance between tooth bodies (i.e. the partbetween the yoke and tooth tip) of two adjacent teeth. The gap betweenadjacent tooth tips should be as small as possible to save as muchmaterial as possible.

The stator core of FIG. 1 can be made by two preferred methods. In afirst method, each lamination layer of the stator core is formed bybending an individual sheet material. In particular, the method formaking the stator core includes the following steps.

Referring to FIG. 2, at step S1, an elongated sheet material is punched.At this time, the sheet material is flat and straight, which includes aconnecting portion and a plurality of teeth extending from theconnecting portion. The teeth are sequentially arranged in the order ofthe first type tooth 1, the second type tooth 2, the third type tooth 3and the fourth type tooth 4. Each tooth includes a tooth body extendingfrom the connecting portion and a tooth tip extending from a distal endof the tooth body to two sides of the tooth body. The tooth tip includesa left half tooth tip and a right half tooth tip. The length of the lefthalf tooth tip and the right half tooth tip is measured in thecircumferential direction of the core.

In order to save material and ensure that the slot opening of thewinding slot is as small as possible after the core laminations arestacked, the gap between adjacent tooth tips should be as small aspossible when in the strip form (before bending). Preferably, the sum ofthe length of the right half tooth tip of the first type tooth and thelength of the left half tooth tip of the second type tooth issubstantially the same as the distance between the first type tooth andthe second type tooth. The sum of the length of the right half tooth tipof the second type tooth and the length of the left half tooth tip ofthe third type tooth is substantially the same as the distance betweenthe second type tooth and the third type tooth. The sum of the length ofthe right half tooth tip of the third type tooth and the length of theleft half tooth tip of the fourth type tooth tip is substantially thesame as the distance between the third type tooth and the first typetooth. The sum of the length of the right half tooth tip of the fourthtype tooth and the length of the left half tooth tip of the first typetooth tip is substantially the same as the distance between the fourthtype tooth and the first type tooth.

Each sheet material after being punched can be considered as beingformed by cutting off a first half of the last tooth group from K+1tooth groups that are sequentially arranged, where K is an integergreater than zero. Each tooth group includes a first type tooth 1, asecond type tooth 2, a third type tooth 3, and a fourth type tooth 4. Ascan be seen from FIG. 2, cutting off a sheet material having 2k+1 toothgroups at a middle of the (k+1)th tooth group can result in a first typelamination 200 a and a second type lamination 200 b. Therefore,preferably, at step S1, the sheet material is first punched to have 2k+1tooth groups, and the sheet material having 2k+1 tooth groups is cut offat the (k+1)th tooth group, thus obtaining a first type lamination and asecond type lamination.

Referring to FIG. 4 and FIG. 5, at step S3, each sheet material is bentinto a ring-shaped lamination, with the connecting portions of all sheetmaterials making the ring-shaped yoke and the teeth of each sheetmaterial extending outwardly from the yoke to form the teeth of thecore.

At step S4, multiple laminations that have been bent into the ring shapeare stacked, with a starting end of a previous lamination overlapping astarting end of a later lamination, and a tail end of the previous layeroverlapping a tail end of the later layer. The first type corelamination 200 a and the second type core lamination 200 b arealternately stacked, either individually or in groups of laminations ofthe same type.

In the method described above, the sheet material is first bent into thering-shaped lamination at step S3 and multiple laminations are thenstacked at step S4. In an alternative embodiment, multiple laminationsare stacked to form multiple layers of laminations at step S3, and thestacked multiple layers of laminations are then bent into the ring shapeat step S4, with the connecting portions of all sheet materials makingthe ring-shaped yoke, and the teeth of each lamination forming the coreteeth extending outwardly from the yoke.

It should be understood that, in the above method, the number of theteeth included in the tooth group is an even number and, after stacking,the first type tooth, second type tooth, third type tooth and fourthtype tooth of multiple layers of laminations overlap with the third typetooth, fourth type tooth, first type tooth, and second type tooth ofother multiple layers.

Referring to FIG. 6, in a second method, the entire magnetic core 100 ismade by rolling or coiling a strip of punched elongated sheet material,multiple turns in a circumferential direction, with each turn beingequivalent to or forming a single lamination layer 200 of the magneticcore 100. In particular, the method includes the following steps.

First, an elongated sheet material is punched to have a connectingportion and multiple teeth extending from the connecting portion. Eachtooth includes a tooth tip extending from a distal end of the tooth onopposite sides of the tooth. The tooth tip has a left half tooth tip anda right half tooth tip. The length of the left half tooth tip and theright half tooth tip is measured in the circumferential direction.

The sheet material after being punched forms a plurality of toothgroups. Each tooth group including a first type tooth 1, a second typetooth 2, a third type tooth 3, and a fourth type tooth 4 that aresequentially arranged. In this embodiment, there are one first typetooth 1, one second type tooth 2, one third type tooth 3, and one fourthtype tooth 4 in each tooth group. In another embodiment, the number ofthe first type teeth and the third type teeth may be more than one.

The sheet material after being punched is rolled or coiled to formmultiple turns, with each turn forming one lamination layer of the motormagnetic core. Each lamination layer includes a ring-shaped yoke andteeth extending outward from the yoke. Each lamination layer includes ktooth groups and a half tooth group that are sequentially arranged. Inthis embodiment, each lamination layer includes 4k+2 teeth. In thismethod, the last two teeth of a previous lamination layer and the firsttwo teeth of a later lamination layer form one tooth group and, thefirst type tooth, the second type tooth, the third type tooth and thefourth type tooth of the previous lamination layer overlap with thethird type tooth, the fourth type tooth, the first type tooth, and thesecond type tooth of the later lamination layer.

The magnetic core of the present invention may be used as a stator coreor a rotor core of the motor.

Understandably, the term “ring shape” as used in this application notonly includes the traditional annular/circular ring shape, but it alsoincludes other shapes such as square or polygonal shape.

Understandably, the present invention may be embodied with eachlamination layer having S teeth, wherein multiple first type teeth, onesecond type tooth, multiple third type teeth and one fourth type tooththat are sequentially arranged to form one tooth group, and each toothgroup has T teeth, with S and T satisfying the following relation:S/T=N+ remainder, where N is a positive integer, T is an even number andremainder=T/2. That is, S/T=N+½ or S=N·T+T/2. Thus the lamination may beformed with an even or odd number of teeth S. Prior to bending the sheetmaterial into the ring shape, the sum of adjacent tooth tips of adjacentteeth is close to (equal to or slightly less than) the distance betweentooth bodies of the adjacent teeth.

Referring to FIG. 7, each tooth group has two first type teeth, onesecond type tooth, two third type teeth, and one fourth type tooth. Assuch, each tooth group has six teeth, and the number of the teeth ofeach lamination layer may be an odd number such as 9, 15 or 21.

Referring to FIG. 8, each tooth group has three first type teeth, onesecond type tooth, three third type teeth, and one fourth type tooth. Assuch, each tooth group has eight teeth, and the number of the teeth ofeach lamination layer may be an even number such as 12, 20 or 28.

In the description and claims of the present application, each of theverbs “comprise”, “include”, “contain” and “have”, and variationsthereof, are used in an inclusive sense, to specify the presence of thestated item or feature but do not preclude the presence of additionalitems or features.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination.

The embodiments described above are provided by way of example only, andvarious other modifications will be apparent to persons skilled in thefield without departing from the scope of the invention as defined bythe appended claims.

The invention claimed is:
 1. A magnetic core for an electric motor,comprising: a ring-shaped yoke; teeth extending outwardly from the yoke,and a tooth tip extending from a distal end of each tooth in acircumferential direction of the core, each tooth tip having a left halftooth tip and a right half tooth tip; wherein the magnetic core has aplurality of lamination layers, each lamination layer comprising:multiple teeth comprising four type teeth sequentially arranged along aclockwise direction having a first type tooth, a second type tooth, athird type tooth and a fourth type tooth, an interval between each twoadjacent teeth being the same, the left half tooth tip of the first typetooth being a short tooth tip, the right half tooth tip of the firsttype tooth being a long tooth tip, the left and right half tooth tips ofthe second type tooth being both short tooth tips, the left half toothtip of the third type tooth being a long tooth tip, the right half toothtip of the third type tooth being a short tooth tip, the left and righthalf tooth tips of the fourth type tooth being both long tooth tips; andwherein, in an axial direction of the motor, the first type tooth of atleast one lamination layer overlaps with the third type tooth of anotherlamination layer, the second type tooth of the at least one laminationlayer overlaps with the fourth type tooth of the another laminationlayer, the third type tooth of the at least one lamination layeroverlaps with the first type tooth of the another lamination layer, andthe fourth type tooth of the at least one lamination layer overlaps withthe second type tooth of the another lamination layer.
 2. The magneticcore of claim 1, wherein each lamination layer includes an even numberof teeth; the magnetic core is formed by stacking multiple layers offirst core laminations and multiple layers of second core laminationsand, in the motor axial direction, the first type tooth, second typetooth, the third type tooth and fourth type tooth of the first corelamination overlap with the third type tooth, fourth type tooth, firsttype tooth, and second type tooth of the second core lamination,respectively.
 3. The magnetic core of claim 1, wherein each laminationlayer has S teeth, wherein multiple first type teeth, one second typetooth, multiple third type teeth and one fourth type tooth aresequentially arranged to form one tooth group, the number of the thirdtype teeth is the same as the number of the first type teeth in eachtooth group, and each tooth group has T teeth, with S and T satisfyingthe following relation: S/T=N+½, where N is a positive integer and T isan even number.
 4. The magnetic core of claim 1, wherein a sum of thelength of the right half tooth tip of the first type tooth and thelength of the left half tooth tip of the second type tooth, a sum of thelength of the right half tooth tip of the second type tooth and thelength of the left half tooth tip of the third type tooth, a sum of thelength of the right half tooth tip of the third type tooth and thelength of the left half tooth tip of the fourth type tooth tip, and asum of the length of the right half tooth tip of the fourth type toothand the length of the left half tooth tip of the first type tooth tipare substantially the same.
 5. The magnetic core of claim 1, wherein themagnetic core is made by spirally rolling an elongated sheet materialmultiple turns, with each turn forming one lamination layer of themagnetic core.
 6. The magnetic core of claim 1, wherein each laminationlayer of the magnetic core is made by bending an individual sheetmaterial.
 7. The magnetic core of claim 1, wherein teeth tips of thefirst type tooth, second type tooth, third type tooth and fourth typetooth are different from each other.
 8. The magnetic core of claim 1,wherein the first type tooth, second type tooth, the third type toothand fourth type tooth form one tooth group, the magnetic core includestwo types of lamination layers, a first type of core lamination isformed by cutting off a first half of a first tooth group from a corelamination having sequentially arranged k+1 tooth groups, and a secondtype of core lamination is formed by cutting off a second half of a lasttooth group from a core lamination having sequentially arranged k+1tooth groups, where k is an integer greater than zero; the first type ofcore lamination and the second type of core lamination are alternatelyarranged.
 9. The magnetic core of claim 8, wherein each tooth groupsatisfies one of the following conditions: (a) each tooth group includesmultiple first type teeth, one second type tooth, multiple third typeteeth, and one fourth type tooth that are sequentially arranged, whereinthe number of the first type teeth is the same as the number of thethird type teeth; (b) each tooth group includes one second type tooth,multiple third type teeth, one fourth type tooth, and multiple firsttype teeth that are sequentially arranged, wherein the number of thefirst type teeth is the same as the number of the third type teeth; (c)each tooth group includes multiple third type teeth, one fourth typetooth, multiple first type teeth, and one second type tooth that aresequentially arranged, wherein the number of the first type teeth is thesame as the number of the third type teeth; (d) each tooth groupincludes one fourth type tooth, multiple first type teeth, one secondtype tooth, and multiple third type teeth that are sequentiallyarranged, wherein the number of the first type teeth is the same as thenumber of the third type teeth.